There are many applications (e.g., analog-to-digital and digital-to-analog conversion) in which the output of an analog circuit is repetitively sampled by a digital circuit which, in turn, changes the input to the analog circuit. Typically, a sequence of steps occur: the digital circuit chooses a digital value; the chosen digital value is applied to the analog circuit (e.g., by converting it to analog and subtracting it from an unknown analog signal); the output of the analog circuit is measured, and, based on the output, the digital circuit chooses a different digital value. The sequence of steps is repeated until the chosen digital value produces a desired result in the analog output (e.g., making the output equal to zero). Often the analog circuit will contain capacitors (or other charge-storage elements) which make the circuit slow to respond to a newly applied input. The digital circuit, on the other hand, is usually faster operating, and thus the time required to complete each sequence of steps is largely controlled by the response time of the analog circuit. For example, if the analog circuit includes a filter for smoothing out ripple and noise, it may require a few seconds for the output of the analog circuit to reach a new value. When these few seconds are multiplied by the number of times the sequence is repeated the lost waiting time can be considerable.